"I know that SX only works with multimode fiber, and that SX operates at a 850-nm wavelength, with LX at a 1300-nm wavelength... but other than that, what are the differences? I suppose I could be confusing things... the reason for my asking is that we are in the process of examining the choices for a SFP transceiver module. That is, the GLC-LH-SM or GLC-SX-MM from Cisco. " From Yahoo answer.

Fiber optic transceivers like SFP can interface with two types of cables, single mode transceiver and multimode transceiver. Single mode like GLC-LH-SM is an optical fiber that will allow only one mode to propagate.The fiber has a very small core diameter of approximately 8 Ám. Multimode like GLC-SX-MM describes a fiber optic cable, which supports the propagation of multiple modes.Multimode fiber may have a typical core diameter of 50 to 100 Ám with a refractive index that is graded or stepped.